1. Field of the Invention
The instant invention relates to an air induction arrangement for improving the combustion characteristics of direct fuel injected diesel engines. More specifically, the instant invention relates to a system whereby the inducted air is guided so as to form a vortical flow within the engine cylinder which mixes with the injected fuel more efficiently.
2. Description of the Prior Art
Among the advantages of direct fuel injected diesel engines are their relatively high thermal and fuel efficiencies. Among their disadvantages is their tendency to produce large quantities of noxious black smoke containing rather large quantities of NOx and HC. This tendency is attributed to the inherent difficulty of mixing the air and fuel during the brief period of the compression stroke.
FIGS. 1 to 3 show two induction port arrangements which are formed in the prior art cylinder heads C and D, respectively. In these arrangements attempts were made to improve combustion by forming the air induction ports in such a manner as to introduce the air into the combustion chamber in the form of a vortical flow to improve the dispersion of the injected fuel with the inducted air.
In the prior art embodiment shown in FIG. 1, the air induction port 100 defines a tapering helix or spiral-shaped arrangement which is defined about the general axis of the valve stem 320. This causes the intake air flow 400 which flows into the combustion chamber past the valve skirt 310, to circulate within the combustion chamber in the form of a vortical flow 410.
In the second prior art arrangement, shown in FIGS. 2 and 3, the air induction port 100 has a helical configuration which terminates at the valve seat of the induction valve 300 so that, as in the FIG. 1 arrangement, the intake air 400 is caused to circulate in the form of a vortical flow 410 upon entering the combustion chamber.
In the above prior art induction passages certain problems are inherent. For example, in the arrangement shown in FIG. 1 the induction port becomes inordinately long. Therefore, when the intake air is heated upstream of the induction valve in order to make the engine easier to start when it's cold, by the time it reaches the combustion chamber a significant amount of heat has been lost to the walls of the air induction port 100 with the result that the pre-heating is partially negated.
In order to reduce the effect of the cylinder walls on temperature of the intake air 400, it is conceivable to form the walls of the air induction port 100 of a ceramic material in an attempt to insulate the intake air 400 from the cylinder head C. Unfortunately, this raises difficulties in that, due to its convolute nature, the forming a ceramic induction port liner which can fit inside of the air induction port 100 of the cylinder head, is difficult and once formed it is nearly impossible to successfully embed in the cylinder head C during the molding process.
During the molding process of the cylinder head D there is also a strong tendency for stresses to become concentrated at the convex portions such as indicated by circle 110 in FIG. 4, resulting in the formation of cracks in the ceramic helical induction port liner.
Another problem with the air induction port 100 comes in that the helical configuration creates a flow resistance which renders it difficult to supply large amounts of air into the combustion chamber and thus lowers the charging efficiency of the system.